• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.8
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• pp.1485-1495
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• 2009

This paper presents a novel approach to economic dispatch (ED) with nonconvex fuel cost function as combinatorial optimization problems (COP) while most of the conventional researches have been developed as function optimization problems (FOP). One nonconvex fuel cost function can be divided into several convex fuel cost functions, and each convex function can be regarded as a generation type (G-type). In that case, ED with nonconvex fuel cost function can be considered as COP finding the best case among all feasible combinations of G-types. In this paper, a genetic algorithm is applied to solve the COP, and the ${\lambda}-P$ function method is used to calculate ED for the fitness function of GA. The ${\lambda}-P$ function method is reviewed briefly and the GA procedure for COP is explained in detail. This paper deals with two kinds of ED problems, namely ED with multiple fuel units (EDMF) and ED with prohibited operating zones (EDPOZ). The proposed method is tested for all the ED problems, and the test results show an improvement in solution cost compared to the results obtained from conventional algorithms.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.1
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• pp.79-87
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• 1998

Basic design of a 50USRT(175㎾) triple effect absorption chiller driven by hot gas has been carried out for both parallel and series flow cycles. Parallel flow cycle showed higher COP, however, the temperature in the generator was also higher than that in series flow cycle. Dynamic operation behavior of a parallel flow system at off-design conditions, such as the change in heat transfer medium temperature or the construction change of the system components, has been investigated in detail. It was found that the cooling capacity was seriously decreased by reducing hot gas flow rate and UA-value in the high temperature generator. However, the system COP was improved, because thermal load in the system components was reduced. The COP and the cooling capacity was found to be improved as cooling water temperature decreased or chilled water temperature increased. The optimum ratio of solution distribution could be suggested by considering the COP, the cooling capacity and the highest temperature in the system, which is critical for corrosion.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.3
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• pp.24-29
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• 2017

In this study, a seat cross member was fabricated by optimizing the resin transfer molding processing of CFRP (Carbon Fiber Reinforced Plastics) materials. This seat cross member is used in automotive underbody parts and provides side impact support. The seat cross was manufactured via vacuum resin transfer molding. The process included 1min of resin injection, 8 mins of heating, and 1 min of cooling, for a total molding time of 10mins. Tensile test results showed an average breaking load of 21.50kN, a tensile strength of 404 MPa, and an elastic modulus of 46.2 GPa. As a result, the CFRP seat cross provides the same strength as a similar steel part, but weighs 42% less.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2006.05a
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• pp.208-213
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• 2006

경사진 안창은 안창의 경사로 발의 자세를 교정함으로써 하지 통증을 완화시키는 데 사용되는 보조치료기구로 내측 경사진 안창(MWI: medially wedged insole)과 외측 경사진 안창(LWI: laterlly wedged insole)으로 나뉜다. 본 연구는 내/외측 경사진 안창이 족부압력에 미치는 영향을 정량적으로 분석하고자 한다. 분석변수는 압력중심(COP: center of pressure)의 궤적 변화, 발바닥 내 세 개 구획에 상대적으로 작용하는 수직 힘(RVF: relative vertical force) 그리고 여덟 개 해부학적 지점의 압력이다. 경사진 안창의 경사조건은 내/외측 각각 $5^{\circ},\;8^{\circ},\;15^{\circ}$이며, 경사가 없는 안창을 포함해 총 일곱 가지 안창이 실험에 사용되었다. 실험참여자로는 20대 성인 남성 10명이 참여하였다. 실험결과 앞발 누름기에서 MWI와 LWI는 모두 COP를 내측으로 이동시키고 외측 압력을 감소시켰다. 뒤축 접지기에서 MWI는 COP를 내측으로 이동 시키고 내측압력을 증가시키는 반면, LWI는 COP를 외측으로 이동시키고 외측압력을 증가시켰다. 그리고 RVF 분석결과 MWI와 LWI는 모두 앞발 부위 힘의 크기를 감소시켰고, LWI만이 발 뒤축 부위 힘의 크기를 증가시켰다.

• Journal of Power System Engineering
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• v.18 no.1
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• pp.57-62
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• 2014

This paper present the performance characteristics of R404A two-stage compression refrigeration system. The operating parameters considered in this study include evaporating and condensing temperature, subcooling and superheating degree, compressor efficiency. The main results were summarized as follows: The COP of two-stage compression refrigeration system using R404A has an effect on the variation of evaporation temperature, condensation temperature, subcooling degree and compressor efficiency, but not an effect on the superheating degree. R404A two-stage compression refrigeration system is unstable because COP of this system is significantly changed when evaporating temperature and compressor efficiency decreased. In particular, when compressor efficiency decreased, COP is significantly decreased. This is inefficient for long-term use.

• Journal of Korean Physical Therapy Science
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• v.19 no.1
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• pp.63-69
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• 2012

Background : The purpose of this study was to investigate the frequency domain characteristics of ground reaction forces during quiet standing on inclined surfaces twenty healthy individuals(10 elderly women $68.78{\pm}3.29$ years and 10 young women $20.90{\pm}0.74$ years) participated. Methods : Subjects stood in quiet stance over a force platform positioned in one of three different fixed positions: flat, down and up. Healthy participants completed with eyes open for 120 s trials. Evaluation of postural control were generally based on the interpretation of center of pressure(COP) time series. The COP have been determined using an experimental setup with 3D kinematic and the ground reaction force system. All the data were expressed means and standard deviation by using SAS package program. Results : SEF 50% were not significant in AP and ML direction according to surface slope of both groups. SEF 95% were showed highest frequency in AP direction on down slope of both groups. MEF were not significant all direction according to surface slopes of elderly women. There was no difference between young and elderly women. Conclusion : Elderly women used to ankle strategy during a quiet stance according to COP perturbation of AP direction showed more expanded than ML direction. SEF 95% were showed highest frequency on down slope in elderly women who showed more used ankle strategy for postural control on down slope.

• PNF and Movement
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• v.8 no.1
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• pp.67-77
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• 2010

Purpose : The purpose of this study was to investigate the usefulness of clinical balance tests through the correlation of balance evaluation using by forceplate in elderly. Methods : Thirty nine healthy elderly subjects (14 males, 25 females) participated in the study. The subjects were evaluated with clinical balance tests [(Berg balance scale (BBS), Functional reach test (FRT), Tinetti's performance oriented mobility assessment (POMA), and one leg standing (OLS)]. Static balance evaluation was assessed by using forceplate. Center of pressure (COP) parameters were obtained using it as total path distance, total sway area, X mean frequency and Y mean frequency for 20 seconds in the following conditions: (1) comfortable standing with eyes opened and closed, (2) uncomfortable standing with eyes opened and closed. After static balance evaluation tested, dynamic balance evaluation was assessed. COP parameters were error distance and area during sine curve trace. COP parameters were movement time, error distance, and maintained time in the circle during COP movement task. Results : Clinical balance tests showed statistically significant correlation between static and dynamic balance evaluations. Among the clinical balance tests, the BBS, POMA, and OLS showed significant correlation with to assess the balance ability of elderly in clinical setting both evaluations. Conclusion : Clinical balance tests can be recommended in clinical setting because of low costs and simplicity.

• Journal of the Korean Solar Energy Society
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• v.34 no.1
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• pp.58-63
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• 2014

A vertical closed loop ground source heat pump (GSHP) is used to produce heat from the low-grade energy source such as the outside air and ground source. It is known that a heat pump system type has better efficiency comparing to the electric heating system. This study only demonstrates that the vertical closed loop GSHP system is a feasible choice for space cooling of air conditioning. The coefficient of performance (COP) is the ratio of heat output to work supplied to the system in the form of electricity. For the vertical closed loop GSHP system in a cooling mode, the COP is the most commonly used way for judging the efficiency. For the purpose of this experiment, vertical closed loop GSHP system was installed in the laboratory and the experiment was executed. As a result, an average COP of vertical-closed loop GSHP system was 3.62 when the outside average temperature was $33^{\circ}C$.

• Journal of Biomedical Engineering Research
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• v.30 no.3
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• pp.255-262
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• 2009

The present study analyzed the association between postural control and electrical stimulation by measuring body sway when use the electrical stimulations were applied to different stimulation zones in lower limbs. The subjects were 14 young adults and were, tested for two different visual condition: eyes open and eyes closed. The experiments were also performed in two different stance case: one legged stance and two legged stance while electrical stimulations were applied concurrently or individually to tibialis anterior and triceps surae. Postural responses were assessed by analyzing COP sway path, sum of COP sway measured by a forceplate. The results showed that the direction of the COP shift changed in accordance with the direction of stimulation and showed sensory adaptation as the experiment progressed for two legged stance case. For one legged stance case, concurrent electrical stimulation both sides of muscles was found to be effective for enhancement of postural balance control.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.9
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• pp.527-535
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• 2009

The aim of this study is to investigate the daily heating performance of ground source multi-heat pump system with vertical single U-tube type GLHXs, which were installed in a school building located in Cheonan. Daily average COP of heat pump unit on Jan. 12th, 2009 at heating mode was lower than it on Nov. 10th, 2008 and Dec. 15th, 2008, because of lower EWT of the outdoor heat exchanger and relatively smaller size of condenser and evaporator. But, the system COP on the former was higher than it on the latter because ground loop circulating pump was operated in rated speed. It is suggested that the new algorithms to control the flow rate of secondary fluid for GLHX according to load change have to be developed in order to enhance the performance of the system COP.